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- /*
- * Distributed under the Boost Software License, Version 1.0.
- * (See accompanying file LICENSE_1_0.txt or copy at
- * http://www.boost.org/LICENSE_1_0.txt)
- *
- * Copyright (c) 2009, 2011 Helge Bahmann
- * Copyright (c) 2009 Phil Endecott
- * Copyright (c) 2013 Tim Blechmann
- * Linux-specific code by Phil Endecott
- * Copyright (c) 2014 Andrey Semashev
- */
- /*!
- * \file atomic/detail/ops_linux_arm.hpp
- *
- * This header contains implementation of the \c operations template.
- */
- #ifndef BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_
- #define BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_
- #include <cstddef>
- #include <boost/memory_order.hpp>
- #include <boost/atomic/detail/config.hpp>
- #include <boost/atomic/detail/storage_type.hpp>
- #include <boost/atomic/detail/operations_fwd.hpp>
- #include <boost/atomic/capabilities.hpp>
- #include <boost/atomic/detail/ops_cas_based.hpp>
- #include <boost/atomic/detail/ops_extending_cas_based.hpp>
- #ifdef BOOST_HAS_PRAGMA_ONCE
- #pragma once
- #endif
- namespace boost {
- namespace atomics {
- namespace detail {
- // Different ARM processors have different atomic instructions. In particular,
- // architecture versions before v6 (which are still in widespread use, e.g. the
- // Intel/Marvell XScale chips like the one in the NSLU2) have only atomic swap.
- // On Linux the kernel provides some support that lets us abstract away from
- // these differences: it provides emulated CAS and barrier functions at special
- // addresses that are guaranteed not to be interrupted by the kernel. Using
- // this facility is slightly slower than inline assembler would be, but much
- // faster than a system call.
- //
- // While this emulated CAS is "strong" in the sense that it does not fail
- // "spuriously" (i.e.: it never fails to perform the exchange when the value
- // found equals the value expected), it does not return the found value on
- // failure. To satisfy the atomic API, compare_exchange_{weak|strong} must
- // return the found value on failure, and we have to manually load this value
- // after the emulated CAS reports failure. This in turn introduces a race
- // between the CAS failing (due to the "wrong" value being found) and subsequently
- // loading (which might turn up the "right" value). From an application's
- // point of view this looks like "spurious failure", and therefore the
- // emulated CAS is only good enough to provide compare_exchange_weak
- // semantics.
- struct linux_arm_cas_base
- {
- static BOOST_CONSTEXPR_OR_CONST bool full_cas_based = true;
- static BOOST_CONSTEXPR_OR_CONST bool is_always_lock_free = true;
- static BOOST_FORCEINLINE void fence_before_store(memory_order order) BOOST_NOEXCEPT
- {
- if ((static_cast< unsigned int >(order) & static_cast< unsigned int >(memory_order_release)) != 0u)
- hardware_full_fence();
- }
- static BOOST_FORCEINLINE void fence_after_store(memory_order order) BOOST_NOEXCEPT
- {
- if (order == memory_order_seq_cst)
- hardware_full_fence();
- }
- static BOOST_FORCEINLINE void fence_after_load(memory_order order) BOOST_NOEXCEPT
- {
- if ((static_cast< unsigned int >(order) & (static_cast< unsigned int >(memory_order_consume) | static_cast< unsigned int >(memory_order_acquire))) != 0u)
- hardware_full_fence();
- }
- static BOOST_FORCEINLINE void hardware_full_fence() BOOST_NOEXCEPT
- {
- typedef void (*kernel_dmb_t)(void);
- ((kernel_dmb_t)0xffff0fa0)();
- }
- };
- template< bool Signed >
- struct linux_arm_cas :
- public linux_arm_cas_base
- {
- typedef typename make_storage_type< 4u >::type storage_type;
- typedef typename make_storage_type< 4u >::aligned aligned_storage_type;
- static BOOST_CONSTEXPR_OR_CONST std::size_t storage_size = 4u;
- static BOOST_CONSTEXPR_OR_CONST bool is_signed = Signed;
- static BOOST_FORCEINLINE void store(storage_type volatile& storage, storage_type v, memory_order order) BOOST_NOEXCEPT
- {
- fence_before_store(order);
- storage = v;
- fence_after_store(order);
- }
- static BOOST_FORCEINLINE storage_type load(storage_type const volatile& storage, memory_order order) BOOST_NOEXCEPT
- {
- storage_type v = storage;
- fence_after_load(order);
- return v;
- }
- static BOOST_FORCEINLINE bool compare_exchange_strong(
- storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order success_order, memory_order failure_order) BOOST_NOEXCEPT
- {
- while (true)
- {
- storage_type tmp = expected;
- if (compare_exchange_weak(storage, tmp, desired, success_order, failure_order))
- return true;
- if (tmp != expected)
- {
- expected = tmp;
- return false;
- }
- }
- }
- static BOOST_FORCEINLINE bool compare_exchange_weak(
- storage_type volatile& storage, storage_type& expected, storage_type desired, memory_order, memory_order) BOOST_NOEXCEPT
- {
- typedef storage_type (*kernel_cmpxchg32_t)(storage_type oldval, storage_type newval, volatile storage_type* ptr);
- if (((kernel_cmpxchg32_t)0xffff0fc0)(expected, desired, &storage) == 0)
- {
- return true;
- }
- else
- {
- expected = storage;
- return false;
- }
- }
- };
- template< bool Signed >
- struct operations< 1u, Signed > :
- public extending_cas_based_operations< cas_based_operations< cas_based_exchange< linux_arm_cas< Signed > > >, 1u, Signed >
- {
- };
- template< bool Signed >
- struct operations< 2u, Signed > :
- public extending_cas_based_operations< cas_based_operations< cas_based_exchange< linux_arm_cas< Signed > > >, 2u, Signed >
- {
- };
- template< bool Signed >
- struct operations< 4u, Signed > :
- public cas_based_operations< cas_based_exchange< linux_arm_cas< Signed > > >
- {
- };
- BOOST_FORCEINLINE void thread_fence(memory_order order) BOOST_NOEXCEPT
- {
- if (order != memory_order_relaxed)
- linux_arm_cas_base::hardware_full_fence();
- }
- BOOST_FORCEINLINE void signal_fence(memory_order order) BOOST_NOEXCEPT
- {
- if (order != memory_order_relaxed)
- __asm__ __volatile__ ("" ::: "memory");
- }
- } // namespace detail
- } // namespace atomics
- } // namespace boost
- #endif // BOOST_ATOMIC_DETAIL_OPS_LINUX_ARM_HPP_INCLUDED_
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